CANBERRA - Australian Greens leader Bob Brown, whose party supports Prime Minister Julia Gillard's minority government, resigned as his party's leader on Friday and announced he would leave parliament in June.

The resignation stunned Greens lawmakers, but will not affect their agreement to support the government.

As a Senator, Brown's resignation also has no impact on the numbers in parliament and will not force a by-election, as his seat will be filled by a Greens replacement who will fill the casual vacancy.

Brown, 67, has been a senator for the island state of Tasmania for 16 years and is the most powerful political figure in Australia outside the ruling Labor party and the opposition Liberal and National parties.

"It is prime time to hand over the reins," Brown said.

He will be replaced as leader by Greens deputy leader Christine Milne.